Most scrolls like that are done with tip 2 or 3. Maybe you just need to apply more pressure (squeeze harder).If that doesn't work, then try a 4. Just keep going up one # until you are satisifiedAlso, often those scrolls are at least 2 layers of icing. Try overpiping the scroll to see it that is the look you want.

This cake was done with a tip 3 http://www.cakecentral.com/cake-photo_1239113.html Stupid me, I never even thought about overpiping!! DUH! I almost always use a tip 3 when doing scroll work and I think that's what size was used in your cake picture too. Practice on waxed paper and then you can reuse the icing until you get the look and size you want!! Also don't fill the bag too full--You'll have more control with just a bit of icing in the bag and your hand won't get so tired. If you're using BC for the scrolls you can also mix in a little corn syrup to make your icing flow smoother and easier! I love scroll work!! Good luck!